GrampsLocale: Clean up _init_from_environment even more

And do it right this time!

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21898 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
GrampsLocale: Ensure self.encoding exists before testing it

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21899 4ae1f11a-8b86-4847-b8af-ab372f36d1fd